Cable boxes or cable cards are required because that is the only way to decode digtal signals. Analog signals take up alot of bandwidth.
Here is a more technical explanation:
Traditional cable providers typically have 550MHz coax systems in smaller markets and 750-850MHz systems in major cities and more densely populated suburban areas. This bandwidth is shared between everything you get on cable, including Internet, TV, VOD, PPV, and phone service. Every analog channel on these systems consumes 6MHz of that bandwidth. If your cable system has 80 analog channels, thatís 480MHz of the system used. On a 550MHz system, that doesnít leave much left for digital channels, high-definition, video-on-demand, or Internet.
Digital transmission is far more efficient than analog tranmission. With digital transmission and compression, cable providers can deliver 8x as many SD channels with equal or better quality ó as analog channels. Cable providers can also fit 2-3 HDTV channels in the same space as one analog channel. Fifty analog channels consumes the same bandwidth as 100-150 full-quality HDTV channels, or more than 200 of the HDTV Lite channels on DirecTV.
Take the theoretical 850MHz digital system. Such a system could support 140 analog channels, but nothing else. An analog channel consumes 6MHz. You can fit 2-3 full-quality HDTV channels in that same 6MHz. An 850MHz system without any analog channels would support more than 1100 standard digital channels or 400 high-definition channels at full quality. This is exactly what Verizon set out to build with its FiOS TV service.
The FiOS fiber optics infrastructure is designed to support up to 10 GBps. Unlike coax cable providers, which divide their bandwidth between Internet, TV, VOD, PPV, and phone service, Verizon dedicates an optical wavelength on its fiber specifically to 850MHz TV service. This RF overlay at 1550nm is used exclusively by FiOS TV service, and is not shared by the Internet, phone, or even video-on-demand.
FiOS TV service uses digital transmission exclusively for its cable channels. There are no analog cable channels on FiOS. FCC rules do require that Verizon provide analog versions of local channels until the switch to digital broadcast television is complete, so FiOS systems do do carry those local channels in analog for now. If you do the math, that means approximately 790MHz of FiOS TV bandwidth is left for digital channels, enough to carry 1050 standard digital channels, 240-400 high-definition channels at full quality, or 500+ of DirecTVís HDTV Lite channels.
Written by fiosfaq
Last updated on 09.17.06